During March, high temperatures broke or tied historical records
at 7,755 locations in the United States out of about 175,000,
according to the National Climatic Data Center (NCDC). By
comparison, only one of the last 10 Marches, in 2007, broke or
tied more than 7,000 record highs.

March has followed in winter's footsteps; the NCDC declared
December, January and February collectively the
fourth-warmest winter on record in the lower 48 states.

Although weather over short periods of time cannot be directly
attributed to human-caused climate change, accumulating
greenhouse gases likely played a role in the " year
without winter " that has graced a significant portion of
North America, according to climate scientists.

"Clearly, this is outstanding and well outside any expectation
under an unchanging climate. The magnitude and duration of the
events in March certainly indicate that some unusual factors are
afoot," Kevin Trenberth, a senior scientist at the
independent National Center for Atmospheric Research (NCAR)
in Boulder, Colo., told LiveScience in an email.

Climate change is one such factor; natural fluctuations represent
the other, Trenberth said.

However, even in a warming world, there will be regions with
below-normal temperatures, Trenberth noted. This March, 287
locations out of 174,643 reported record lows or tied with
historic ones. These were clustered largely in the western United
States.

The mild
winter temperatures arose this year as a result of the
configuration of the jet stream— high-altitude, westerly winds
that have kept cold, Arctic air bottled up farther north,
according to meteorologists and climate scientists. The jet
stream, in turn, was influenced by natural patterns, such as air
pressure over the Arctic.

"Extremes are always expected to happen as the climate record
gets longer, but certain extremes related to heating are becoming
more evident. For example, in the United States, extremes of high
temperatures have been occurring at a rate of twice those of cold
extremes and that has accelerated considerably since June 2010 to
a factor of 2.7, and in the summer of 2011 to a factor of over
8," Trenberth wrote in an article published online in the journal
Climatic Change on March 21.